The purposes of this study are to investigate in detail the mechanical properties of bone, both normal bone subject to biochemical alteration in the laboratory and pathologic bone derived from metabolic manipulation of the skeleton in vivo in the laboratory animal, and finally to initiate a study of the mechanical properties of pathological bone derived from human autopsies in conditions that are known to have major skeletal involvement as an inherent part of the disease process, particularly renal osteodystrophy. We are principally interested in examining those parameters which describe both the quantitative and qualitative aspects of bone tissue failure. These quantities include the yield-stress for the tissue under tensile and compressive loading, the modes of failure in tension, compression and shear loading and the amount of energy that the tissue can absorb up to the point of initiation of plastic deformation and the point of gross tissue disruption.